Medicinal Plants for Skin Disorders

Bioassay-guided fractionation of the shoots of a medicinal plant belonging to Myrsinaceae led to the isolation of a new compound, ‘Myricetin-3-O-(2'',4''-diacetyl)-α-L-rhamnopyranoside’, along with 12 known metabolites. This is the first report on the isolation of six compounds from the shoots of the plant. The compounds’ structures were elucidated by different spectroscopic methods including 1D, 2D NMR experiments and HR-ESI-MS analysis. In order to identify natural tyrosinase inhibitors and antioxidant agents, these isolated compounds were evaluated for their anti-tyrosinase and antioxidant activities. All the compounds exhibited good tyrosinase inhibitions, whereas, compounds 4, 10, 11 and 12 showed excellent anti-tyrosinase activities with fifty percent inhibitory concentrations (IC₅₀) values of 43.90, 24.94, 35.00, and 26.20 µg/ml, respectively. The anti-tyrosinase activity of myrisinoside A, myrisinoside B, myricetin, mearnsetin 3-O-(4″-O-acetyl)-rhamnopyranoside, mearnsitrin, myricetin 3-O-(4″-O-acetyl) rhamnopyranoside and quercetin 3-(3'',4''-diacetyl-rhamnoside) have been reported for the first time. Compounds 1-12 also displayed excellent antioxidant activities with IC₅₀ values ranging from 0.92-1.85 µg/ml. This is the first report on the DPPH radical scavenging activity of myrisinoside A, myrisinoside B, mearnsetin 3-O-(4″-O-acetyl)-rhamnopyranoside, myricetin 3-O-(4″-O-acetyl) rhamnopyranoside and quercetin 3-(3'',4''-diacetyl-rhamnoside).

 The effects of plant on the expression of the tyrosinase gene and on melanin transfer were also evaluated.  It was concluded that the inhibition of melanin by the plant was post-transcriptional. The mechanism of action of the extract was further substantiated by in the melanin transfer assay where melanosomes containing melanin were not found to be transferred between the melanocytes and keratinocytes, indicating inhibition at a possible protein level.